这里有新鲜出炉的Python3 官方中文指南,程序狗速度看过来!
Python 是一种面向对象、解释型计算机程序设计语言,由Guido van Rossum于1989年底发明,第一个公开发行版发行于1991年。Python语法简洁而清晰,具有丰富和强大的类库。它常被昵称为胶水语言,它能够把用其他语言制作的各种模块(尤其是C/C++)很轻松地联结在一起。
在之前学习python设计模式(工厂模式实践篇),希望使用全局变量代替c++的宏完成服务自动注册功能时,遇到过一个问题,全局变量的定义和使用放在同一个可执行脚本中的问题
先把有问题的代码晒一下:
IServer.py
- from abc import ABCMeta, abstractmethod
- print __name__
- class IServer:
- def __init__(self):
- pass
- @abstractmethod
- def DoWithA(self):
- pass
- @abstractmethod
- def DoWithB(self):
- pass
IServer_A.py
- import IServer
- serverType ='1001'
- print __name__
- dir()
- from CreatFactory import GLOBAL_class_dic
- dir()
- class IServer_A(IServer.IServer):
- def __init__(self):
- pass
- def DoWithA(self):
- print 'Server_A do with interface A'
- def DoWithB(self):
- print 'Server_A do with interface B'
- global GLOBAL_class_dic
- print 'the id of GLOBAL_class_dic in A is:',id(GLOBAL_class_dic)
- GLOBAL_class_dic[serverType] = IServer_A
- print 'GLOBAL_class_dic in a is:', GLOBAL_class_dic
IServer_B.py
- import IServer
- serverType ='1002'from CreatFactory import GLOBAL_class_dic
- print __name__
- class IServer_B(IServer.IServer):
- def __init__(self):
- pass
- def DoWithA(self):
- print 'Server_B do with interface A'
- def DoWithB(self):
- print 'Server_B do with interface B'
- print 'the id of GLOBAL_class_dic in B is:',id(GLOBAL_class_dic)
- GLOBAL_class_dic[serverType] = IServer_B
- print 'GLOBAL_class_dic in b is:', GLOBAL_class_dic
CreatFactory.py
- #coding:UTF-8
- import os;
- import sys;
- import threading
- from misc import *
- global GLOBAL_class_dic
- GLOBAL_class_dic ={1:1}
- print 'GLOBAL_class_dic in define is:', GLOBAL_class_dic
- print 'the id of GLOBAL_class_dic in define is:', id(GLOBAL_class_dic)
- dir()
- import IServer_A
- import IServer_B
- def CreateServer(serverType):
- global GLOBAL_class_dic
- print 'GLOBAL_class_dic in use is:', GLOBAL_class_dic
- print 'the id of GLOBAL_class_dic in USE is:', id(GLOBAL_class_dic)
- if GLOBAL_class_dic.has_key(serverType):
- return GLOBAL_class_dic[serverType]
- else:
- return 'no'
- if __name__ == '__main__':
- pass
- # 接收到报文后,根据报文的内容,从db中获取到serverType,假设获取到的serverType=1001
- print 'main'
- print 'GLOBAL_class_dic in main A is:', GLOBAL_class_dic
- serverType = '1002'
- server = CreateServer(serverType)
- print 'GLOBAL_class_dic in main B is:', GLOBAL_class_dic
- print 'server :',server
- server.DoWithA(server())
代码内已经加了调试的部分信息, 运行CreatFactory.py。调用DoWithA失败,提示AttributeError: 'str' object has no attribute 'DoWithA'。运行结果如下:
- D: \Python27\python.exe "D:/DesignMode/Server --00/CreatFactory.py"GLOBAL_class_dic in define is: {
- 1 : 1
- }
- the id of GLOBAL_class_dic in define is: 36230176['GLOBAL_class_dic', 'Misc', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'binascii', 'inspect', 'minidom', 'os', 'struct', 'sys', 'threading'] IServer IServer_A['IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType'] GLOBAL_class_dic in define is: {
- 1 : 1
- }
- the id of GLOBAL_class_dic in define is: 36230032['GLOBAL_class_dic', 'Misc', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'binascii', 'inspect', 'minidom', 'os', 'struct', 'sys', 'threading']['IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType']['GLOBAL_class_dic', 'IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType'] IServer_B the id of GLOBAL_class_dic in B is: 36230032 GLOBAL_class_dic in b is: {
- 1 : 1,
- '1002': <class IServer_B.IServer_B at 0x022C2ED8 >
- } ['GLOBAL_class_dic', 'IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType'] the id of GLOBAL_class_dic in A is: 36230032 GLOBAL_class_dic in a is: {
- 1 : 1,
- '1002': <class IServer_B.IServer_B at 0x022C2ED8 > ,
- '1001': <class IServer_A.IServer_A at 0x02273420 >
- }
- main GLOBAL_class_dic in main A is: {
- 1 : 1
- }
- GLOBAL_class_dic in use is: {
- 1 : 1
- }
- the id of GLOBAL_class_dic in USE is: 36230176 GLOBAL_class_dic in main B is: {
- 1 : 1
- }
- server: no Traceback(most recent call last) : File "D:/DesignMode/Server --00/CreatFactory.py",
- line 38,
- in<module > server.DoWithA(server()) AttributeError: 'str'object has no attribute 'DoWithA'
- Process finished with exit code 1
从运行的结果,可以看到:GLOBAL_class_dic 被定义了2次。有两个不同的id,第一次定义分配了一块内存,第二次不明原因的又重新分配了一块内存,然后服务的自动注册全部注册在这块内存中,等到main函数使用的使用,又使用的是第一次申请的内存,所以导致程序运行失败。那问题就来了,为什么会被重新又分配了一次?
之所以会被重新定义一次全局变量,是因为在执行CreatFactory.py时,最开始定义了全局变量,此时该命名空间可使用的函数和变量打印:['GLOBAL_class_dic', 'Misc', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'binascii', 'inspect', 'minidom', 'os', 'struct', 'sys', 'threading',然后在import IServer_A,在IServer_A.py中,import IServer后,在from CreatFactory import GLOBAL_class_dic打印出可使用的函数和变量时,['IServer', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'serverType'],就没有GLOBAL_class_dic,程序发现没有,就又重新声明了一遍。似乎问题原因已经找到了。
python在导入的时候,有2种场景,一种就是在文件前普通的import语句,还有一种就是特殊的场景:__main__模块是相对于Python的导入系统。在最开始运行CreatFactory.py文件时,__name__打印的值是__main__,而再子类再次导入时,会在当前命名空间查找是否已经导入__name__=CreatFactory,发现这个模块不存在,故此又导入了一遍,全局变量由此又被重新定义分配了内存,后期全局变量在子类业务的使用就都使用该值,而在main函数里,使用的又是当前的作用域内的第一次定义的全局变量。
来源: http://www.phperz.com/article/17/1028/350929.html